This invention relates to equipment used in the drilling and completion of subterranean wells, and more specifically to a tool tie-down for use with tools and equipment lowered into subterranean wells.
The procedure for drilling and completing subterranean wells to recover, for example, oil and gas from a reservoir, consists of boring a hole in the earth down to the reservoir of interest and installing pipe from the reservoir to the surface. Casing is used as a protective liner within the well bore that is cemented in place to insure a pressure-tight connection to the oil and gas reserve. The casing consists of lengths of tubulars, or joints. Casing is run into the well bore one joint at a time. The unfinished well bore has rough sides of raw earth, and, on occasion, the casing becomes stuck against irregularities in the sides of the well bore as it is lowered down. When this occurs, the casing may be forced down the well bore by adding load to the casing string to force the casing down, by circulating fluid down the interior of the casing so that the fluid exits the casing into the annular space between the external side of the casing and the sides of the well bore to free the casing from the well bore, or by a combination of adding load and circulating drilling fluid. To accomplish this, a tool, such as a circulating tool, may be attached to the top end of the casing string.
Drilling fluid is added to the casing string also to provide counter-pressure against the interior walls of the casing string to prevent the casing from being crushed by the high pressures encountered in the well bore. For this use of drilling fluid, the top end of the casing string, at the surface of the well bore, must be sealed as the fluid is added so that sufficient pressure is maintained inside the casing string. To accomplish this, a fill-up tool may be attached to the top of the casing string.
Circulation and fill-up functions may also be provided by a unitary fill-up and circulating tool such as that described in U.S. Pat. No. 5,584,343, issued Dec. 17, 1996.
Another operation for completing finishing a subterranean well is to cement the casing to the wellbore to seal the casing to the earth formation once the casing string is in place. Cementing is typically accomplished by removing the fill-up or circulating tool and installing a cementing head or plug container to the top of the casing. The cementing head is used to pump cement down the casing string and into the annulus between the outside of the casing and the sides of the wellbore until the annulus is filled with cement and a pressure tight seal is obtained. Elastomeric cement plugs are well known in the art of cementing casing or other tubulars in well boreholes. Such plugs are routinely used to wipe the interior of a casing string, and can be used as a mechanical separation between two types of fluids, for example, between drilling fluids and cement. The plug wipes the inside of the casing and separates the cement from the drilling fluid below.
Tools for cementing operations, fill-up, and circulating are attached to the top of the casing string and at least some portion of the tool may be lowered inside the top of the casing string for a particular operation. In such circumstances, the tool may experience high pressures from the wellbore. These pressures act to force the tool up and out of the casing. Traditionally, such tools are prevented from being pushed out of the casing merely by the traveling block to which the tool is attached and the hook or other assembly which attaches the tool to the traveling block. Sometimes the traveling block may have a push plate to push the tubular into the borehole. These traditional structures do not secure the tool in its position in the casing, nor do they xe2x80x9ctie-downxe2x80x9d the tool to prevent the tool from being ejected from the casing by down hole pressures. The traveling block, hook or push plate are simply the first structures in the way of the tool if it does get ejected from the casing. Ejection of a tool from the casing can be explosive when it occurs, causing substantial damage to the tool and to any structure in its trajectory. To prevent tool ejection and to protect the tool and the rig structures above the tool from catastrophic damage due to tool ejection, it would be useful to have a tool tie-down that resists the upward forces acting on the lowered tool and that secures the tool in a desired position at the top of the casing string.
An example of a tool which is commonly lowered into the top of the casing from a rig and whose operation would benefit from being tied down is a fill-up and circulate (xe2x80x9cFACxe2x80x9d) tool, such as that described in U.S. Pat. No. 5,584,343, issued Dec. 17, 1996, to Malcolm G. Coone (Davis-Lynch, Inc., Pearland, Tex.), which is incorporated herein by reference in its entirety. When the FAC tool of the ""343 patent is inside the casing in a circulate mode, the sealing element or packer of the FAC tool engages the inside of the casing or well bore to create a seal to prevent the escape of fluids from below to above the seal. These fluids are thus under a pressurized condition and act on the FAC tool to push it in an upward direction.
For a FAC tool for standard rotary type rigs, such as described in the ""343 patent, the only constraint preventing the seal from being pushed out of the top of the casing when circulating is the top of the FAC tool assembly pushing against the hook on the traveling block of the rig.
Even though the FAC tool is guided to some extent by a yoke mechanism attached to the bails, the yoke has no holding power against an upward force to help keep the seal in the casing when upward pressure is applied from below the seal. Therefore, the weight of the hook and traveling block is the only downward force keeping the seal inside the casing under pressure from below.
During circulation, the FAC tool is placed in a compression mode, by the pressure from below the seal pushing upwardly. The top of the FAC tool pushes against the rounded portion of the bottom of the traveling block/tool. This causes the FAC tool to be unstable in the presence of strong upward pushing or compression forces. Thus, this type of assembly limits the amount of pressure that can be applied below the seal or packer element of the FAC tool.
Pressure applied from below a FAC tool that has been tied using the tie-down tool also puts the FAC tool in compression. However, in accordance with the invention, the upwardly directed force is absorbed by a pair of cords fabricated, for example from an elastomer, a metal or metal alloy, a fiber, or combinations thereof tied back to the bottom eyes of the bails. These cords, in turn, are attached, directly or indirectly, to the elevator or traveling block. The cords redirect the upward force due to the pressure from below and use it to hold the force due to this pressure from below being applied directly to the traveling block hook. This redirection of the upward or pressure from below force is thus absorbed by the tool of the present invention. Proper sizing of the cords, and/or selection of suitable cord materials, fabricated, for example, from steel or a steel alloy, allows for higher pressures to be exerted from below the FAC tool seal.
Therefore, provided herein is a tie-down tool comprising a tie-down yoke assembly securable to a rig, and one or more cords securable to the tie-down yoke assembly and to the tool-lowering slips of the rig, to secure a tool in a desired position inside the top end of the casing.
The invention is best understood by the following detailed description taken in conjunction with the drawings. These are intended as only illustrative and not limitative, as the invention may admit to other embodiments to these of skill in the art.